Waterjet propulsion of marine vessels has many benefits over propeller propulsion. However, a disadvantage is the lack of lateral directional stability, especially at slow speed, which is a result of not having a rudder and skegs in the water under the aft portion of the vessel. This, in combination with the natural lag in waterjet nozzle steering response, causes “fish-tailing”. In propeller-driven craft, the rudder, skegs, strut and propeller cooperate to provide lateral stability and suppress excessive course deviations from a straight course. A waterjet-powered vessel must compensate by steering nozzle action to maintain a straight course.
It is possible to correct for the absence of this passive lateral stability by actively manipulating the waterjet steering nozzle to keep the vessel going in a straight line. However, it requires a much greater concentration on steering on the part of the operator than is needed for equivalent rudder-steered vessels. This takes the operator's attention away from vigilance required for safe navigation, especially at slow speed in narrow waters with high traffic volume. If this higher attention to steering is not provided, the vessel will follow a wandering or “fish-tailing” path instead of the straight line that is desired. Moreover the vessel safety is compromised if the operator can not apply full attention to navigation.
The present invention seeks to alleviate this higher attention demand for steering by assisting the operator in preventing over-steering that takes place in an effort to make the vessel progress in a straight course. The “natural” time lag mentioned above is the time between the operator's action to make a directional correction and his first observation of a directional change of the vessel which resulted from such correction. Since the response is not immediate, as with a rudder, the operator will increase the excursion of the correction (over-steer) because he sees no apparent result of his original action. The result is a major degree of overshoot from the intended course of the vessel, requiring considerable corrective action of the steering wheel in the opposite direction, resulting again in overshooting the intended course in the opposite direction. The sequence repeats itself time after time resulting in an “S” shaped or “fish-tail” course instead of a straight one.
By learning to steer the vessel in correction increments, namely by holding a steering correction for a few seconds and then returning the wheel to center before the correction gets out of hand, a major directional excursion can be prevented and the vessel can be steered in a straight line. However, such steering strategy takes a great deal of the operator's attention, especially if he cannot tell where the exact center position of the steering nozzle is. It is therefore of great importance that the operator be able to determine where the steering center position is. It is equally important for the operator to know on which side of the center position he is holding the steering wheel, if not at the center position.
A visual indicator can be used but this again requires the operator to take his attention away from navigation and look at a dial on the dashboard. Then, it will take concentration to return the wheel to the exact center position. This further defeats the purpose of maintaining the operator's attention on navigation and traffic as much as possible.